Endovascular delivery catheters are used to implant prosthetic devices, such as a prosthetic valve, at locations inside the body that are not readily accessible by surgery or where access without surgery is desirable. The usefulness of delivery catheters is largely limited by the ability of the catheter to successfully navigate through small vessels and around tight bends in the vasculature, such as around the aortic arch.
Known delivery apparatuses include a balloon catheter having an inflatable balloon that mounts a prosthetic valve in a crimped state and a retractable cover that extends over the valve to protect the interior walls of the vasculature as the valve is advanced to the implantation site. Various techniques have been employed to adjust the curvature of a section of the delivery apparatus to help “steer” the valve through bends in the vasculature. The balloon catheter may also include a tapered tip portion mounted distal to the balloon to facilitate tracking through the vasculature. The tip portion, however, increases the length of the relatively stiff, non-steerable section of the apparatus. Unfortunately, due to the relatively long stiff section, successful delivery of a prosthetic valve through tortuous vasculature, such as required for retrograde delivery of a prosthetic aortic heart valve, has proven to be difficult.
A known technique for adjusting the curvature of a delivery apparatus employs a pull wire having a distal end fixedly secured to the steerable section and a proximal end operatively connected to a rotatable adjustment knob located outside the body. Rotation of the adjustment applies a pulling force on the pull wire, which in turn causes the steerable section to bend. The rotation of the adjustment knob produces less than 1:1 movement of the pull wire; that is, rotation of the knob does not produce equal movement of the steerable section. To facilitate steering, it would be desirable to provide an adjustment mechanism that can produce substantially 1:1 movement of the steerable section.
It is also known to use an introducer sheath for safely introducing a delivery apparatus into the patient's vasculature (e.g., the femoral artery). An introducer sheath has an elongated sleeve that is inserted into the vasculature and a seal housing that contains one or more sealing valves that allow a delivery apparatus to be placed in fluid communication with the vasculature with minimal blood loss. A conventional introducer sheath typically requires a tubular loader to be inserted through the seals in the sheath housing to provide an unobstructed path through the seal housing for a valve mounted on a balloon catheter. A conventional loader extends from the proximal end of the introducer sheath, and therefore decreases the available working length of the delivery apparatus that can be inserted through the sheath and into the body.
Accordingly, there remains a need in the art for improved endovascular systems for implanting valves and other prosthetic devices.